In general, in a broadband wireless communication system, a base station allocates resources to each terminal for transmission and reception of packets. The base station then sends MAP message, which indicates resource assignment results, such as location and size of an allocated resource, modulation method, encoding rate and the like, to the terminal via a downlink channel. Here, the resource allocation is performed with respect to resources within a specific interval, accordingly, MAP Information Element (IE) is sent at each of the specific interval.
However, for a service for periodically sending packets with the same size, such as a Voice Over Internet Protocol (VoIP) service, transmission of MAP IEs with the same contents at every time of sending a packet causes resource consumption.
Hence, for a service having a specific transmission period, a persistent allocation for persistently allocating resources may be applied so as to decrease resource consumption due to the MAP IEs. According to the persistent allocation technology, for downlink communication, MAP IE and packet are sent only upon initial resource allocation, and thereafter only packets are sent without the MAP IE. Therefore, a terminal using a persistently allocated resource keeps using the persistently allocated resource without a MAP IE until receiving allocation release information or allocation change information. Here, for the sake of explanation, the persistently allocated resource is referred to as ‘persistent resource.’
Table 1 shows an example of MAP IE including parameters for allocation persistent resources to a terminal.
TABLE 1SyntaxSize(bit)Scription/NotesDL PersistentAllocationA-MAP_IE( ){A-MAP IE Type 4DL Persistent Allocation A-MAP IEAllocation Period 2Period of persistent allocation.If(Allocation Period=0b00), it indicates the deallocation ofa persistently allocated resource.0b00:deallocation0b01:2 frames0b10:4 frames0b11:8 frames...Resource Index115 MHz: 0 in first 2 MSB bits + 9 bits for resourceindex10 MHz: 11 bits for resource index20 MHz: 11 bits for resource indexResource index includes location and allocation sizeLong TTI Indicator 1Indicates number of subframes spanned by the allocatedresource.0b0: 1 subframe (default)0b1: 4 DL subframes for FDD or all DL subframes for TDDHFA 6HARQ Feedback AllocationACID 4HARQ channel identifier. N_ACIDs: Number of ACIDs forimplicit cycling of HARQ channel identifierN_ACID=Floor{ PA_Max_ReTx_Delay/ (AllocationPeriod*Frame_length) }+1...
In Table 1, ‘HARQ Channel Identifier (ACID)’ field indicates ACID for identifying (distinguishing) HARQ processes performed using allocated resources.
Here, the HARQ process denotes a process performed until one HARQ packet is successfully received, and includes initial transmission, retransmission, combining and the like, in association with the one HARQ packet. Therefore, HARQ packets belonging to the same HARQ process may include the same ACID. Here, the ACID may be called as HARQ process ID. That is, the ACID is an identifier for allowing a terminal to work a plurality of HARQ processes in parallel, and a plurality of HARQ processes belonging to one terminal are granted different ACIDs. Hence, for combining an initially transmitted packet and a retransmitted packet, a receiving end combines HARQ packets having the same ACID.
In general, in order to use the ACID, ‘start or initial ACID’ and ‘the number of ACIDs (N_ACID)’ are needed. For example, if the initial ACID is 3 and the number of ACIDs is 3, ACIDs 3, 4 and 5 are circularly used as ACIDs of an allocated persistent resource. In other words, if the number of ACIDs is 3, maximum three of HARQ processes are worked in one persistent resource, and ACIDs of the three HARQ processes are set to 3, 4 and 5.
More concretely, ACID of the first HARQ process is set to 3, ACID of the second HARQ process is set to 4 and ACID of the third HARQ process is set to 5. If a fourth HARQ process is generated, ACID of the fourth HARQ process is set to 3. For allocation of persistent resources, the base station sends MAP IE one time at the beginning, so the terminal implicitly applies ACIDs in the order of 3, 4 and 5. Here, as aforesaid, since the first and fourth HARQ processes use the same ACID, the first HARQ process should be terminated prior to starting the fourth HARQ process.
In other words, HARQ packet of the first HARQ process should be successfully received prior to receiving HARQ packet of the fourth HARQ process, and HARQ channel corresponding to the ACID of the first HARQ process should be flushed to store the HARQ packet of the fourth HARQ process.
That is, the maximum number of HARQ transmission and the number of ACIDs are in a functional relation therebetween. Hence, upon circularly running the ACIDs, the sufficiently large number of ACIDs must be present to avoid duplication (repetition) of ACIDs. Also, the number of HARQ processes simultaneously used for one persistent resource and the number of ACIDs may be transferred while a terminal and a base station establish a connection therebetween or via a Broadcast Channel (BCH) periodically sent by the base station.
FIG. 1 is a flowchart showing a typical persistent resource allocation method for allocating ACIDs to data burst via DL PA A-MAP IE.
First, in order to allocate persistent resources to a terminal, a base station sends DL PA A-MAP IE including persistent resource allocation information to the terminal (S101).
Here, the base station may send the DL PA A-MAP IE to the terminal to allocate a new persistent resource or change a previously allocated persistent resource.
In order to allocate the new persistent resource to the terminal, the base station may send the DL PA A-MAP IE to a subframe, which is different from a subframe of a previous allocated persistent resource.
In addition, upon sending the DL PA A-MAP IE to the same subframe as the subframe of the previously allocated persistent resource, the base station intends to reallocate the previously allocated persistent resource other than allocating a new persistent resource.
As shown in FIG. 1, the base station sends the DL PA A-MAP IE to the terminal to allocate a new persistent resource to the terminal.
The DL PA A-MAP IE sent by the base station includes information related to an initial ACID value needed for allocating ACID in a persistent resource allocation and information related to the number of ACIDs available for the persistent resource allocation. That is, the initial ACID value and the ACID number value are included in ACID field of the DL PA A-MAP IE to be sent to the terminal.
The initial ACID value is set in consideration of ACID values being used at the time point of the persistent resource allocation and the number of consecutively available ACIDs.
The base station also decides the number of ACIDs available for the persistent resource allocation using persistent resource allocation information included in the DL PA A-MAP IE, namely, allocation period and system parameters (e.g., Tproc, LongTTI Indicator, Frame_length, N_MAX-ReTx).
For example, using Table 1, in case of initial ACID (included in DL Persistent A-MAP) value=0, process time (Tproc)=3, LongTTI Indicator=1, Frame_length=5 ms, Allocation Period (0b10)=4 frames and N_MAX-ReTx=8, the decided results are PA_ReTx_Interval=10 ms, PA_Max_ReTx_Delay=8*10=80 ms, and N_ACID=Floor{80 ms/(4*5)}+1=5.
Therefore, the ACID values used in the corresponding persistent resource allocation are 0, 1, 2, 3 and 4.
FIG. 1 shows that the initial ACID value is ‘0’ and N_ACID value is ‘3.’
Referring to FIG. 1, if the initial ACID value and the N_ACID value both included in the DL PA A-MAP IE are ‘0’ and ‘3,’ respectively, ACID values available for the persistent resource allocation are 0, 1 and 2 (S102).
Therefore, the base station allocates the initial ACID value ‘0’ included in the DL PA A-MAP IE to the first DL burst, which is sent in an area indicated by the DL PA A-MAP IE (S103-1).
Next, the base station allocates ACID values to DL bursts (second, third, . . . ), succeeding the first DL burst, using the N_ACID value 3 (i.e., 0, 1, 2) with increasing the ACID value by one in a cycling manner (S103-2˜S103-4).
That is, the base station repeats the process of allocating ACID ‘0’ to the first DL burst sent in the area indicated by the DL PA A-MAP IE, ACID ‘1’ to the second DL burst, ACID ‘2’ to the third DL burst and circularly ACID ‘0’ to the fourth DL burst (S103).
Here, when the persistent resource is reallocated by the DL PA A-MAP IE, the terminal updates previously set persistent resource allocation information to the new persistent resource allocation information included in the DL PA A-MAP IE.
However, in case where the base station reallocates a persistent resource to the terminal with respect to a previously allocated persistent resource using the above method, the currently retransmitted ACID value may be problematically the same as ACID value used for reallocation.
Especially, when ACID value different from ACID value prior to reallocation is not able to be used as ACID value used for reallocation, the following problems may occur.
For example, when a persistent resource having ACID values 0, 1, 2, 3 and 4 has been allocated, if reallocation is generated at a time point of ACID value=‘2,’ and the reallocation is performed by setting the initial ACID value to ‘2’ and N_ACID value to ‘5,’ ACID values used for the reallocation are 2, 3, 4, 5 and 6.
However, when five ACID values cannot consecutively be allocated among ACID values from 5 to 15, namely, the currently used ACID values are 5, 9, 10 and 15, the base station should reallocate five ACID values from 0 to 4.
Here, if a packet whose ACID value is 0 is being retransmitted, a packet corresponding to the previously allocated ACID value ‘0’ and the packet corresponding to the currently reallocated ACID value ‘0’ have the same ACID value, accordingly, the terminal and the base station cannot perform an appropriate operation for the corresponding persistent resource allocation.